KR101932823B1 - Improved oled stability via doped hole transport layer - Google Patents

Abstract

The present invention provides an organic light emitting device. The device includes an anode and a cathode. A first organic layer is disposed between the anode and the cathode. The first organic layer is a light-emitting layer including the first organic luminescent material. The apparatus also includes a second organic layer disposed between the anode and the first organic layer. The second organic layer is a non-light emitting layer. The second organic layer includes an organic small molecule hole transporting material having a concentration of 50 to 99 wt% and an organic small molecule electron transporting material having a concentration of 0.1 to 5 wt%. Other materials may also be present.

Description

IMPROVED OLED STABILITY VIA DOPED HOLE TRANSPORT LAYER [0002]

This application claims the benefit and priority of U.S. Provisional Application No. 61 / 121,991, filed December 12, 2008, under 35 USC § 119 (e), which is expressly incorporated herein by reference in its entirety.

The claimed invention was performed in conjunction with and / or on behalf of one or more of these organizations in accordance with the joint industry-academic research conventions of the Regents of the University of Michigan, Princeton University, The University of Southern California, and Universal Display Corporation. The Convention entered into force on and before the date on which the claimed invention was made and the claimed invention was made as a result of activities undertaken within the scope of the Convention.

- Technology -

The present invention relates to organic light emitting devices, and improved components for such devices.

BACKGROUND OF THE INVENTION [0002] Optoelectronic devices using organic materials are being valued for a number of reasons. Many of the materials used to fabricate such devices are relatively inexpensive, and thus organic optoelectronic devices have the potential of cost advantages over inorganic devices. In addition, thanks to the inherent properties of organic materials, such as their flexibility, they can be suitable for the production of certain applications, such as elastic substrates. Examples of organic optoelectronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. In the case of OLEDs, organic materials can have performance advantages over conventional materials. For example, the wavelength at which the organic light emitting layer emits light can be easily tuned using a suitable dopant.

OLEDs use an organic thin film that emits light when a voltage is applied across the device. OLEDs are of increasing interest as a technology for use in fields such as, for example, flat displays, lighting, and backlighting. Several OLED materials and configurations are described in U.S. Patent Nos. 5,844,363, 6,303,238 and 5,707,745, which are incorporated herein by reference in their entirety.

One of the applications of phosphorescent emitting molecules is full-color display. The industry standard for such displays requires pixels that are adjusted to emit a particular color, called "saturated" color. Specifically, this standard requires saturated red, green, and blue pixels. The color can be measured using CIE coordinates well known in the art.

An example of a green emitting molecule is tris (2-phenylpyridine) iridium, designated Ir (ppy) ₃ , having the structure of formula (I)

Here, and in the following drawings, the inventors of the present invention express a bond which is spatially separated from a nitrogen atom to a metal (here, Ir) by a straight line.

The term "organic" as used herein includes polymeric materials as well as small molecule organic materials that can be used to fabricate organic optoelectronic devices. "Small molecule" means any organic material that is not a polymer, and "small molecule" may actually be very large. Small molecules may contain repeat units in some situations. For example, a molecule using a long chain alkyl group as a substituent is not removed from the "small molecule" class. Small molecules may also be introduced into the polymer, for example, as a pendant group on the polymer backbone or as part of the backbone. The small molecule may also be provided as a core moiety of a dendrimer, consisting of a series of chemical shells built on a core moiety. The core moiety of the dendrimer may be a fluorescent or phosphorescent small molecule emitter. Dendrimers can be "small molecules", and all dendrimers currently used in the field of OLEDs are considered small molecules.

As used herein, "top" means the extreme from the substrate, while "bottom" means closest to the substrate. When the first layer is described as being "over " the second layer, the first layer is disposed away from the substrate. Other layers may be present between the first and second layers, unless it is specified that the first layer is "in contact with the second layer ". For example, a cathode may be described as being "placed on " the anode, although there may be various organic layers between them.

As used herein, "solution processible" means that it can be dissolved, dispersed or transported in a liquid medium, in the form of a solution or suspension, and / or deposited from a liquid medium.

The ligand can be said to be "photoactive" when the ligand is considered to contribute directly to the photoactivity of the emitting material. A ligand is said to be "secondary" when the ligand is not believed to contribute to the photoactivity of the emitting material, but ancillary ligands may alter the properties of the photoactive ligand.

As used herein and as generally understood by those skilled in the art, the first energy level "HOMO" or "Lowest Unoccupied Molecular Orbital" (LUMO) energy level is defined as the energy level at which the first energy level is at a vacuum energy level Is "greater" or "higher" than the second HOMO or LUMO energy level. Since the ionization potential (IP) is measured as negative energy with respect to the degree of vacuum, the high HOMO energy level corresponds to IP with a smaller absolute value (less negative IP). Similarly, a high LUMO energy level corresponds to an electron affinity with a smaller absolute value (less negative EA). In a typical energy level chart, the degree of vacuum is above and the LUMO energy level of the material is higher than the HOMO energy level of the same material. A "high" HOMO or LUMO energy level appears closer to the top of this chart than a "low" HOMO or LUMO energy level.

As used herein, and as those skilled in the art will appreciate, the first work function is "greater" or "higher" than the second work function if the first work function has a high absolute value. Since the work function is usually measured as a negative number for the degree of vacuum, the "high" work function means a more negative value. In a typical energy level chart, the degree of vacuum is at the top and the "high" work function is marked farther away from the degree of vacuum downward. Thus, the definitions of the HOMO and LUMO energy levels follow a convention different from the work function.

A more detailed description of the OLED, and the above-described definition, can be found in U.S. Patent No. 7,279,704, incorporated herein by reference in its entirety.

An organic light emitting device is provided. The apparatus includes an anode and a cathode. The first organic layer is disposed between the anode and the cathode. The first organic layer is a light-emitting layer including the first organic luminescent material. The apparatus also includes a second organic layer disposed between the anode and the first organic layer. The second organic layer is a non-light emitting layer. The second organic layer includes an organic small molecule hole transporting material having a concentration of 50 to 99 wt% and an organic small molecule electron transporting material having a concentration of 0.1 to 5 wt%. Other materials may be present.

Preferably, the concentration of the organic small molecule molecular electron transporting material in the second organic layer is 0.1 to 4% by weight, more preferably 2 to 4% by weight. Even more preferably, the concentration of the organic small molecule molecular electron transporting material in the second organic layer is 0.1 to 3% by weight, more preferably 2 to 3% by weight. Preferably, the second organic layer is in direct contact with the first organic layer.

In one embodiment, the apparatus further comprises a third organic layer disposed between the second organic layer and the anode, and the third organic layer comprises a hole injecting material. In one embodiment, the third organic layer is in direct contact with the anode and the second organic layer.

In one embodiment, the apparatus further comprises a fourth organic layer disposed between the first organic layer and the cathode, and the fourth organic layer is a light emitting layer comprising the second light emitting material.

In one embodiment, the apparatus further comprises a fifth organic layer disposed between the second organic layer and the anode, wherein the fifth organic layer comprises an organic small molecule hole transport material, but does not include an organic small molecule molecular electron transport material.

In one embodiment, the organic small molecule electron transport material has a HOMO-LUMO difference of at least 0.2 eV above the HOMO-LUMO difference of the organic small molecule hole transport material.

In one embodiment, the LUMO energy level of the organic small molecule molecular electron transporting material is lower than the LUMO energy level of the organic small molecule hole transporting material by at least 0.2 eV.

Preferably, the first organic luminescent material is phosphorescent.

In one embodiment, the luminescent material has a peak emission wavelength in the visible spectrum of 600 to 700 nm. In another embodiment, the luminescent material has a peak emission wavelength in the visible spectrum of 500 to 600 nm. In another embodiment, the luminescent material has a peak emission wavelength in the visible spectrum of 400 to 500 nm.

A preferred class of materials for organic small molecule molecular electron transport materials is metal quinolate. The Alq ₃ is a preferred metal quinol rate. LG201 is also a preferred organic small molecule molecular electron transport material.

A preferred material class for organic small molecule hole transport materials is amine containing materials. NPD is the preferred amine containing material.

Preferably, the organic small molecule electron transport material has higher electron mobility than the organic small molecule hole transport material.

1 is a view showing an organic light emitting device.
2 is a view showing an inverted organic light emitting device having no individual electron transporting layer.
3 is a view showing an organic light emitting device having a non-light emitting layer doped with an electron transporting material.
4 is a diagram showing an organic light emitting device having a non-light emitting layer doped with an electron transporting material, and another special layer.
5 is a view showing a specific organic light emitting device structure including a non-light emitting layer doped with an electron transporting material.
6 is a view showing a specific organic light emitting device structure including a non-light emitting layer doped with an electron transporting material.
7 is a view showing a specific organic light emitting device structure including a non-light emitting layer doped with an electron transporting material.

In general, the OLED includes at least one organic layer disposed between the anode and the cathode and electrically connected to the anode and the cathode. When an electric current is applied, the anode injects holes and the cathode injects electrons into the organic layer (s). The injected holes and electrons move to the opposite charged electrodes, respectively. When electrons and holes are localized on the same molecule, an exciton is formed which is a localized electron-hole pair with an excited energy state. Light is emitted when excitons are relaxed through the photoemissive mechanism. In some cases, the excitons can be localized on an excimer or exciplex. Non-radioactive mechanisms, such as thermal relaxation, may also occur, but are generally considered to be undesirable.

Early OLEDs use luminescent molecules that emit light from their singlet state ("fluorescent emission"), as disclosed, for example, in U.S. Patent No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs within a time period of less than 10 nanoseconds.

More recently, an OLED having a luminescent material that emits light from a triplet state ("phosphorescence") has been identified. Baldo et al., "Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices," Nature, vol. 395, 151-154, 1998; ("Baldo-I") and Baldo et al., "Very high-efficiency green organic light-emitting devices based on electrophosphorescence," Appl. Phys. Lett., Vol. 75, No. 3, 4-6 (1999) ("Baldo-II"), incorporated herein by reference in its entirety. Phosphorescence is described in more detail in U.S. Patent No. 7,279,704 at column 5-6, incorporated herein by reference.

FIG. 1 is a view showing an organic light emitting device 100. FIG. This figure is not necessarily drawn to scale. The device 100 includes a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, a light emitting layer 135, a hole blocking layer 140, 145, an electron injection layer 150, a protective layer 155, and a cathode 160. [ The cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Apparatus 100 may be fabricated by depositing the layers described in order. The properties and functions of these various layers as well as exemplary materials are described in more detail in U.S. Patent No. 7,279,704, columns 6-10, and incorporated herein by reference.

More examples of each of these layers can be used. For example, an elastic and transparent substrate-anode combination is disclosed in U.S. Patent No. 5,844,363, incorporated herein by reference in its entirety. An example of a p-doped hole transporting layer is disclosed in US Patent Application Publication No. 2003/0230980, which is incorporated herein by reference in its entirety, and which is doped with F 4-TCNQ in a molar ratio of 50: 1 m-MTDATA. Examples of release and host materials are disclosed in U.S. Patent No. 6,303,238 (Thompson et al), which is incorporated herein by reference in its entirety. An example of an n-doped electron transporting layer is Li-doped BPhen in a ratio of 1: 1, as disclosed in U.S. Published Patent Application 2003/0230980, which is incorporated herein by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, incorporated herein by reference in their entirety, disclose a cathode comprising an overlaid transparent, conductive, compound cathode with a thin layer of metal such as Mg: Ag with a sputter-deposited ITO layer . ≪ / RTI > The uses and theories of the barrier layer are described in more detail in U.S. Patent No. 6,097,147 and U.S. Published Patent Application 2003/0230980, which are hereby incorporated by reference in their entirety. An example of an injection layer is provided in U.S. Published Patent Application 2004/0174116, which is incorporated herein by reference in its entirety. The description of the protective layer can be found in US Published Patent Application 2004/0174116, which is incorporated herein by reference in its entirety.

2 is a diagram illustrating an inverted OLED 200. FIG. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Apparatus 200 may be fabricated by depositing the layers described in order. The device 200 is referred to as an "inverted" OLED because the most common OLED configuration is that of placing a cathode on the anode and the device 200 having the cathode 215 under the anode 230 . Materials similar to those described for device 100 may be used in the corresponding layers of device 200. FIG. 2 provides an example of how some layers may be omitted in the structure of the device 100. FIG.

It should be understood that the simple laminated structure as illustrated in Figures 1 and 2 is provided by way of non-limiting example, and embodiments of the present invention may be used in conjunction with various other structures. The specific materials and structures described are exemplary in nature and other materials and structures may be used. Functional OLEDs may be obtained by combining the various layers described in various manners, based on design, performance and price factors, or may omit the layers as a whole. Other layers not specifically described may also be included. Other materials than those specifically mentioned may be used. While many of the examples provided herein describe the various layers as comprising a single material, it is understood that combinations of materials may be used, such as a mixture of host and dopant, or a more general mixture. In addition, the layers can have various sublayers. The nomenclature given to the various layers herein is not intended to be limiting in any way. For example, in the device 200, the hole transport layer 225 transports holes and injects holes into the light emitting layer 220, so that the device can be referred to as a hole transport layer or a hole injection layer. In one embodiment, the OLED can be described as having an "organic layer" disposed between the anode and the cathode. Such an organic layer may comprise a single layer, or it may comprise a plurality of layers of different organic materials, for example as described in Figures 1 and 2. [

Structures and materials not specifically described may also be used and OLEDs including polymeric materials (PLEDs) as disclosed in U.S. Patent No. 5,247,190 (Friend et al), incorporated herein by reference in its entirety, may also be used. As a further example, an OLED having a single organic layer can be used. OLEDs may be stacked, for example, as described in U.S. Patent No. 5,707,745 (Forrest et al.), Which is incorporated herein by reference in its entirety. The OLED structure may deviate from a simple laminated structure as illustrated in Figs. 1 and 2. For example, the substrate may include respective reflective surfaces to enhance out-coupling, such as the mesa structure described in U.S. Patent No. 6,091,195 (Forrest et al.), And / or U.S. Patent No. 5,834,893 (Bulovic et al. ), Which are incorporated herein by reference in their entirety.

Unless otherwise specified, any of the layers of the various embodiments may be deposited in any suitable manner. In the case of an organic layer, preferred methods are described in U.S. Patent No. 6,337,102 (Forrest et al.), Which is incorporated herein by reference in its entirety, including the thermal evaporation method, the ink-jet method as described in U.S. Patent Nos. 6,013,982 and 6,087,196, (OVPD), as described in U.S. Patent Application Serial No. 10 / 233,470, and deposition by OVPP, as described in U.S. Published Patent Application No. 10 / 233,470, incorporated herein by reference in its entirety . Other suitable deposition methods include spin coating and other solution-based processes. The solution-based process is preferably carried out in a nitrogen or inert atmosphere. For other layers, the preferred method involves thermal evaporation. Preferred patterning methods include masks such as those described in U.S. Patent Nos. 6,294,398 and 6,468,819, incorporated herein by reference in their entirety, deposition via cold welding, and patterning in connection with some deposition methods such as inkjets and OVJD. Other methods can be used. The deposited material may be modified to be compatible with the particular deposition method. For example, substituents such as those containing alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons can be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 or more carbon atoms may be used, and the preferred range of carbon atoms is 3-20. A material with an asymmetric structure may have a better solution processability than a material with a symmetric structure, since an asymmetric material may be less prone to recrystallization. Dendrimer substituents can be used to improve the ability of small molecules to undergo solution processing.

Devices manufactured in accordance with embodiments of the present invention may be used in various applications such as flat panel displays, computer monitors, televisions, billboards, internal or external lighting and / or signal lights, head up displays, fully transparent displays, elastic displays, laser printers, , A laptop computer, a digital camera, a camcorder, a viewfinder, a microdisplay, a vehicle, a large area wall, a theater or stadium screen, or a sign. Various control mechanisms can be used to control the devices fabricated in accordance with the present invention, including passive and active matrices. Numerous devices are intended for use in humans in a comfortable temperature range, such as 18 [deg.] C to 30 [deg.] C, more preferably room temperature (20-25 [deg.] C).

The materials and structures described herein can find applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors can apply such materials and structures. More generally, organic devices, such as organic transistors, can apply such materials and structures.

The term halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylalkyl, heterocyclic groups, aryl, aromatic groups, and heteroaryl are known in the art and are defined in columns 31-32 of U.S. Patent No. 7,279,704 , Which are incorporated herein by reference.

An organic light emitting device is provided. The apparatus includes an anode and a cathode. The first organic layer is disposed between the anode and the cathode. The first organic layer is a light-emitting layer including the first organic luminescent material. The apparatus also includes a second organic layer disposed between the anode and the first organic layer. The second organic layer is a non-light emitting layer. The second organic layer includes an organic small molecule hole transporting material having a concentration of 50 to 99 wt% and an organic small molecule electron transporting material having a concentration of 0.1 to 5 wt%. Other materials may be present.

Using the described structure, the OLED lifetime was improved by more than two times as compared to devices that did not include the organic small molecule molecular electron transport material in the second organic layer. The second organic layer is closer to the anode than the light emitting layer, and thus transports the holes to the light emitting layer. It may be somewhat counterintuitive to introduce an electron transporting material into this layer in significant amounts because the electron transporting material is expected to undesirably increase the operating voltage of the device because it dilutes the hole transporting material, This is true in many situations. However, when used at the right concentrations in small molecular organic devices, this undesirable increase in operating voltage is more than offset by a desirable increase in device life. The concentration of the organic small molecule molecular electron transporting material in the second organic layer is in the range of 0.1 to 5 wt%, preferably 0.1 to 4 wt%, when the exchange between the increase in the device life and the increase in the operating voltage is expected to be very advantageous for a wide range of materials. Range, 2 to 4 wt%, more preferably 0.1 to 3 wt%, and even more preferably 2 to 3 wt%.

Without wishing to be bound by any theory as to why some embodiments of the present invention may be practiced, it is believed that many commonly used, or highly desirable, hole transport materials are vulnerable to damage from electrons and / or excitons. These hole transporting materials are generally used on the anode side of the device where hole transport is the main transport mechanism and electrons and excitons are relatively uncommon but relatively low concentrations of electrons or excitons are required in excess time to provide sufficient hole transport It is thought to be able to damage molecules. For example, an electron concentration of 10 ⁶ less than the hole concentration may be thought to result in such damage.

One particular failure mechanism may be the formation of an exciton on the hole transport material by electron or exciton leakage from the adjacent EML layer to the HTL. Electrons can recombine with holes on hole transport molecules and form excitons. The use of an electron transporting material as a dopant in a hole transporting layer in which an electron transporting material has a lower luminous energy than that of a hole transporting material and in which a light emitting spectrum of a hole transporting and an electron transporting material are superimposed on each other causes energy transfer from the hole transporting material to the electron transporting material . In such a situation, the hole transporting material can be relaxed to a bottom state as the exciton is formed on the electron transporting material. The presence of excitons on the electron transporting material is not destructive to the device stability as much as the presence of the excitons on the hole transporting material. The excitons on the electron transporting material can then be decayed, preferably non-radioactively, but small amounts of radioactive decay can withstand unless significantly affecting the device spectrum.

Another specific failure mechanism may be the formation of an excited state of hole transport material filled molecule (radical anion or polaron) due to absorption of light and / or electron leakage from the light emitting layer to the hole transport layer. In such a case, the anionic state of the hole transporting material may be destructive to the device. The electron transporting material present in the hole transporting layer can transport the electrons thoroughly to the hole transporting layer and prevent the recombination of holes and electrons on the hole transporting material molecules. Preferably, the electron transporting material is at least 0.2 eV, and the LUMO energy is lower than that of the hole transporting material, ensuring that the electrons of the hole transporting layer preferentially migrate and stay in the electron transporting material.

For example, it is believed that the triarylamine hole transport material is decomposed in some devices due to the leakage of electrons and excitons from the light emitting layer, which causes total device degradation during operation.

It may be useful to introduce a small amount of electron transport material, which can also quench the excitons. Alq ₃ is an example of such a material. Improvement in device lifetime may be due to quenching of the NPD excited state molecules formed due to electron or exciton leakage from the EML interface to the NPD HTL. Another mechanism responsible for lifetime enhancement is the transport of an excess amount of electrons through a hole transport layer, such as NPD, with an electron transport material, such as Alq ₃ , which avoids recombination of holes and electrons on the same NPD molecule. In order to utilize this transportation mechanism, it is preferable that there is a single hole transporting layer which consistently extends from the light emitting layer to the anode, or possibly to the hole injecting layer, and the electron transporting material exists throughout the hole transporting material. However, in some embodiments, there may be not only a hole transporting layer including an electron transporting layer but also a hole transporting layer not containing an electron transporting material. In this example, in many devices, only the degradation of molecules in or immediately adjacent to the luminescent layer would be considered to have the greatest influence on the device lifetime, so that only the device life could be improved.

At a desired concentration, the introduction of a small amount of electron transport material into the hole transport layer improves device lifetime and has less effect on device spectra and voltage efficiency characteristics. This idea was tested in green and red phosphorescent OLEDs with NPD HTL doped with 2-10% Alq. Alq was chosen as an electron transport material because it has lower excited state energy than NPD and easily accepts excitons from NPD. Alq can also transport an excess amount of electrons (leaks from the EML) through the HTL to avoid electron damage to the NPD HTL. However, it is believed that a broad combination of hole transport and electron transport materials will have similar results. The test results show that a concentration of less than or equal to 5 wt%, preferably less than or equal to 4 wt%, and more preferably less than or equal to 3 wt%, avoids undesirable effects that occur when the concentration of the electron transporting material in the hole transport layer becomes excessively high Which is desirable.

Preferably, the second organic layer is in direct contact with the first organic layer. The non-light emitting layer immediately above the anode surface of the light emitting layer, that is, the non-light emitting layer in contact with the light emitting layer, is expected to have the highest electron density on the anode surface of the light emitting layer. This is a layer in which the presence of a small concentration of electron transporting material is most advantageous.

The amine containing material is any organic material including amine groups. Amine containing materials are a preferred class of hole transport materials for OLEDs due to their excellent hole transport properties. Triarylamines, and in particular NPD, are preferred amine containing materials and are used as hole transport materials in many OLED configurations. However, the amine containing material is sensitive to damage due to electrons and excitons as described above. NPD and other triarylamine hole transporting materials are believed to be particularly chemically unstable in the excited state (anion state or exciton state), which is a major cause of short lifetime in devices using a trilylarylamine hole transport material. The amine containing material is the preferred hole transport material for use in some embodiments of the present invention.

Metal quinolate is a preferred class of electron transport materials for OLEDs due to their excellent electron transport properties. Alq ₃ is the preferred metal quinolate and is used as an electron transporting material in many OLED configurations. Metal quinolate is a preferred electron transporting material for use in some embodiments of the present invention.

"Non-luminescent" means that the layer contributes to the luminescence of the device in a non-luminescent manner. "Non-luminescent" means that the material is not luminescent in the device, although it may be luminescent in other situations. One way to determine whether the electron transport dopant in the non-luminescent hole transport layer is "non-luminescent" is to measure the shift in the 1931 CIE coordinates of the doping device for the control device. For example, if the device having a specific electron transporting dopant in the hole transport layer has 1931 CIE coordinates at (0.005, 0.005) in the same device without dopant, the dopant can be considered "non-luminescent ". Preferably, any movement in the 1931 CIE coordinates may be less than (0.003, 0.003). It is believed that many electron transporting materials, if doped into the hole transporting layer, can undesirably cause emission from the layer and / or if the range is higher than that disclosed herein, can result in high operating voltages. Preferably, the concentration of the small molecule organic electron transporting material in the second organic layer is 5 wt% or less, preferably 4 wt% or less, more preferably 3 wt% or less.

In one embodiment, the apparatus further comprises a third organic layer disposed between the second organic layer and the anode, and the third organic layer comprises a hole injecting material. In one embodiment, the third organic layer is in direct contact with the anode and the second organic layer. The third organic layer can act as a hole injection layer, which readily accepts holes from the anode and injects them into the rest of the device.

In one embodiment, the apparatus further comprises a fourth organic layer disposed between the first organic layer and the cathode, and the fourth organic layer is a light emitting layer comprising the second light emitting material. The use of such a fourth organic layer advantageously allows the use of multiple light emitting materials in OLEDs, which can be used to produce OLEDs having a broad emission spectrum and / or white light.

In one embodiment, the apparatus further comprises a fifth organic layer disposed between the second organic layer and the anode, and the fifth organic layer comprises an organic small molecule hole transport material, but does not include an organic small molecule molecular transport material. Since the organic small molecule electron transporting material is not present in all places where the organic small molecule hole transporting material exists, this particular example is advantageous in that the advantageous effect of the small molecule electron transporting material in the hole transporting layer is that the electron transporting material On the contrary, it is most useful in a situation where it is judged to be due to an electron transporting material serving as a recombination site for electrons. By limiting the presence of the small molecule organic electron transporting material in the region near the light emitting layer, any harmful effect of the small molecule organic electron transporting material on the device operating voltage can be further minimized.

In one embodiment, the organic small molecule electron transport material has a HOMO-LUMO difference of at least 0.2 eV lower than the HOMO-LUMO difference of the organic small molecule hole transport material. The small HOMO-LUMO difference of the organic small molecule molecular electron transport material allows the organic small molecule electron transport material to easily accommodate the exciton from the organic small molecule hole transport material while the exciton transport in the opposite direction can be a less common event . It is believed that the presence of excitons on organic small molecule electron transport materials is much less detrimental to device performance than the presence of excitons on organic small molecule hole transport materials.

In one embodiment, the LUMO energy level of the organic small molecule molecular electron transporting material is lower than the LUMO energy level of the organic small molecule hole transporting material by at least 0.2 eV. The low LUMO energy level of the organic small molecule electron transporting material is such that the organic small molecule electron transporting material readily accepts electrons from the organic small molecule hole transporting material or leaks any electrons leaking from the light emitting layer to the hole transporting layer, It makes it possible to accept it more preferentially than material. The presence of electrons on the organic small molecule electron transporting material is considered to be far less harmful to the device performance than the presence of electrons on the organic small molecule hole transporting material.

Preferably, the first organic luminescent material is phosphorescent. The compositions disclosed herein may be particularly useful in devices that use phosphorescent emitters as opposed to fluorescent emitters. In general, phosphorescent emitters have significantly longer exciton lifetimes than exciton lifetimes in fluorescent devices. As a result, exciton migration from molecule to molecule and exciton leakage into adjacent layers, such as the hole transport layer, may be more in phosphorescent devices. Therefore, one of the problems that arise with the use of organic small molecule molecular electron transport materials in the hole transport layer can be much more common in phosphorescent devices.

In one embodiment, the luminescent material has a peak emission wavelength in the visible spectrum of 600 to 700 nm. In another embodiment, the luminescent material has a peak emission wavelength in the visible spectrum of 500 to 600 nm. In another embodiment, the luminescent material has a peak emission wavelength in the visible spectrum of 400 to 500 nm. One advantageous aspect of the concentrations disclosed herein for the use of organic small molecule electron transport materials in the hole transport layer is that the organic small molecule electron transport layer will not emit significantly. Many desirable organic small molecule electron transport materials, such as Alq ₃ , can emit in some situations. Alq ₃ specifically emits green light. It may not be excessively harmful that a green light is emitted from an unintended material as a light emitting material in an apparatus for emitting green light. However, in an apparatus in which an intended light emitting material emits red or blue light, it is not preferable that green light is emitted from the material in the transporting layer.

A preferred class of materials for organic small molecule electronic transport materials is metal quinolate. The Alq ₃ is a preferred metal quinol rate. LG201 is also a preferred organic small molecule molecular electron transport material.

A preferred class of materials for organic small molecule hole transport materials is amine containing materials. NPD is the preferred amine containing material.

Preferably, the organic small molecule electron transport material has higher electron mobility than the organic small molecule hole transport material. Those skilled in the art will generally know that the material can be an excellent electron transport change or an excellent hole transport. Bipolar, and a small number of materials capable of transporting electrons and holes, but the most common materials are excellent electron carriers or excellent electron carriers. The reference measure for whether a material is an electron transporting material or a hole transporting material is the electron and hole mobility of the layer made of that material. The electron transporting material layer generally has at least one more electron mobility than its hole mobility. Another way to measure whether a material is an electron transport material is to make some similar devices that use the material in the electron transport layer. The devices are the same except that the thickness of the electron transporting layer is different. By measuring and comparing the current-voltage characteristics of the device, the electron transporting property of the electron transporting material can be quantified. In addition, a number of known families of electron transport materials are described in Table 1 below.

3 is a view showing an apparatus 300 equipped with a non-light emitting layer which is a hole transporting layer doped with an electron transporting material. Apparatus 300 includes an anode 320 and a cathode 380. A first organic layer 350, which is a light emitting layer comprising a first organic luminescent material, is disposed between the anode 320 and the cathode 380. The second organic layer 340, which is a non-emitting layer, includes an organic small molecule hole transporting material doped with an organic small molecule electron transporting material. The second organic layer 340, which is located between the anode 320 and the first organic layer 350, is a hole transport layer. The device 300 may also include other layers 330 and 370, which may be any of various organic layers used in the OLED, as the case may be. For example, layer 370 may represent at least one of a hole and / or exciton blocking layer, an electron transporting layer, and an electron injecting layer. For example, layer 370 may represent at least one of a hole transport layer and a hole injection layer in addition to the second organic layer 340. Examples of such layers are illustrated in Figures 1 and 2. Other types of layers may also be present.

4 is a diagram illustrating an apparatus 400. Device 400 is similar to device 300 and similarly includes an anode 320, a cathode 380, a first organic layer 350, and a second organic layer 340. Apparatus 400 further illustrates layer 330 of apparatus 300. Specifically, the device 400 includes a hole injection layer 331 and a hole transport layer 332 which are disposed in order on the anode 320. [ The hole transport layer 332 preferably includes the same small molecule hole transport material as the second organic layer 340 but in contrast to the second organic layer 340 the hole transport layer 332 does not include an electron transport material.

FIG. 5 is a diagram illustrating an apparatus 500. Apparatus 500 illustrates specific layers and material choices used in experiments involving green light emitting devices. The device 500 includes an anode 510 which is an ITO layer with a thickness of 80 Å, a hole injection layer 520 which is a LG-101 layer with a thickness of 100 Å, a hole transport layer 530 with a thickness of 300 Å, a compound doped with 10% Emitting layer 540 which is a 300 Å thick layer of B, an electron transporting layer 550 which is a 100 Å thick layer of Compound A, another electron transporting layer 560 which is a 300 Å thick layer of LG-201, and a cathode of LiF / Al 570). Compound A is a green phosphorescent emitting material in device 500.

FIG. 6 is a diagram illustrating an apparatus 600. Apparatus 600 illustrates specific layer and material choices used in experiments involving red light emitting devices. The device 600 includes an anode 510 which is a 800 Å thick ITO layer, a hole injecting layer 620 which is a 100 Å thick layer of LG-101, a hole transporting layer 630 of 400 Å thick, A light emitting layer 640 which is a 300 Å thick layer of BAlq B, another electron transporting layer 650 which is a 550 Å thick layer of LG-201, and a cathode 660 which is LiF / Al. Compound C is a red phosphorescent emitting material in device 600.

FIG. 7 is a diagram illustrating an apparatus 700. Apparatus 700 illustrates specific layers and material choices used in experiments involving green light emitting devices. The device 700 comprises an anode 710 which is a 800 Å thick layer of ITO, a hole injection layer 720 which is a 100 Å thick layer of compound A, a hole transport layer 730 which is 300 Å thick, A light emitting layer 740 which is a 300 Å thick layer of compound B, an electron transporting layer 750 which is a 100 Å thick layer of compound B, another electron transporting layer 760 which is a 400 Å thick layer of Alq ₃ and a cathode which is LiF / 770). Compound A is a green phosphorescent emitting material in device 700.

Combination with other materials

The materials described herein as being useful for a particular layer in an organic light emitting device can be used in combination with various other materials present in the device. For example, the luminescent dopants disclosed herein can be used together in a variety of hosts, transport layers, barrier layers, implant layers, electrodes, and other layers that may be present. The materials described or cited below are non-limiting examples of materials that can be used in combination with the compounds disclosed herein, and those skilled in the art will be able to review the literature and identify other materials that can be used in combination.

Many hole injecting materials, hole transporting materials, host materials, dopant materials, exciton / hole blocking layer materials, electron transporting and electron injecting materials can be used in OLEDs in addition to and / or in combination with the materials disclosed herein. Non-limiting examples of materials that can be used in OLEDs in combination with the materials disclosed herein are listed in Table 1 below. Table 1 lists non-limiting material classes, examples of non-limiting examples of each class, and references disclosing the materials.

As used herein, the following compounds refer to materials having the following structure:

LG-201 is a compound that can be purchased from LG Chem Korea. "NPD" means N, N'-di (1-naphthyl) -N, N'-diphenylbenzidine. "Alq ₃ " means tris (8-hydroxyquinoline) aluminum. BAlq means aluminum (III) bis (2-methyl-8-quinolinato) 4-phenyl phenolate.

Experiment

The lifetime of green and red phosphorescent OLEDs with triarylamine HTL (NPD) was improved by more than 2x by doping HTL with 2% metal quinolate (Alq) as compared to an undoped NPD HTL reference device. All doping ratios are% by weight. All of the measurements reported in Tables 2, 3 and 4 were performed at room temperature. Improvement in device lifetime may be due to quenching of NPD excited state molecules formed due to electron or exciton leakage from EML to NPD HTL. The doped HTL appeared to work in both the green and red phosphorescent OLEDs without contamination of the device EL spectra and showed that the doped HTL is suitable for use in typical layer configurations for R, G, and B OLEDs.

The experimental results are shown in Tables 2 and 3. Table 2 shows data for a green phosphorescent OLED having the structure shown in FIG. 5, which is specific to all materials except HTL. The HTL materials are provided in Table 2. The green phosphorescent OLED was fabricated using NPD HTL (Comparative Example 1) NPD: 2% Alq ₃ (Example 1), and NPD: 10% Alq ₃ (Example 2). The addition of the 2% Alq ₃ dopant to the NPD HTL significantly improved lifetime without significantly changing device color, efficiency and voltage (more than 2x for the product of lifetime x luminance ² [Gnits * h] Most OLEDs have an inverse power law dependence on lifetime where the luminescence lifetime is 1 / luminescence ⁿ (where n is typically between 1.5 and 2.5) Proportional). An additional increase in the Alq ₃ dopant concentration in the HTL further extended the device lifetime at 40 mA / cm 2. However, there was also a significant negative impact on device voltage, efficiency and initial luminescence. The following tables show that at 80% (LT ₈₀ ) of the initial luminescence at the initial luminescence L _o measured by the luminous efficiency (candelas / amp), the external quantum efficiency (%), the power efficiency (lumens per Watt) provide a 90% (on) there is a time required to collapse (LT ₉₀₎ of luminance, where the initial current flow was measured by a 40 mA / ㎠, the life time of the product of Gnits ² x ² emission property. Table 2 below shows the performance results of a green phosphorescent OLED with a doped HTL.

It is possible that Alq ₃ is a green emitter, and that unwanted emission from Alq _{3 in} HTL is generally not visible in green phosphorescent OLEDs. For this reason, a red light emitting device with BAlq: compound C EML was prepared on NPD HTL (Comparative Example 2), NPD: 2% Alq ₃ (Example 3), and NPD: 5% Alq ₃ (Example 4). Table 3 shows data for these red phosphorescent OLEDs having the structure shown in FIG. 6, which is specific to all materials except HTL. HTL materials are provided in Table 3. The incorporation of the Alq ₃ dopant into the NPD HTL at a concentration of up to 5% by weight had no significant change in the device CIE. Device performance did not change significantly. These results show that NPD doped with Alq ₃ can be used as an HTL in devices emitting light other than green.

It is also not expected that the effect of the dopant concentration on the measured voltage, efficiency and initial luminescence will be significantly changed due to device color. Tables 2 and 3 together thus show that device lifetimes can be increased without significant negative impact on voltage, efficiency and initial luminescence using dopant concentrations of up to 5 wt%, while high dopant concentrations, such as 10 wt% It is possible to make a significant negative impact. Based on the reasons for selecting the materials, i.e., the hole and electron transport properties of the material, it is believed that this conclusion can be broadly extended for electron and hole transport materials as a whole. Table 3 shows the performance results of a red phosphorescent OLED with a doped HTL.

Table 4 shows the performance results of a green phosphorescent OLED with a doped HTL.

Table 4 shows data for a green phosphorescent OLED having the structure shown in FIG. 7, which is specific to all materials except HTL. The HTL material is provided in Table 4. The green phosphorescent OLED was fabricated using NPD HTL doped with LG-201 at 2 and 5 wt.% (Examples 5 and 6) and was found to be more stable than Comparative Example 3 with undoped NPD HTL. Apparatus Examples 7 and 8 have a split HTL: 150 Å undoped NPD and 150 Å LG-201 doped NPD, where the doped region is close to the EML layer. These devices are also more stable than the Comparative Example 3 reference device. The data in Table 4 is an enlargement of the results presented in Tables 2 and 3 to the dopant material LG201, and LG201 is known to be an excellent electron transport material and is not considered metal quinolate.

It is understood that the various embodiments described herein are by way of example only and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without departing from the scope of the present invention. Accordingly, the claimed invention includes modifications from the specific examples and preferred embodiments described herein, which are obvious to those skilled in the art. It is to be understood that the various teachings of the present invention are not intended to be limiting.

Claims (20)

Anode;
Cathode;
A first organic layer disposed between the anode and the cathode, the first organic layer being a light emitting layer comprising a first organic luminescent material;
A second organic layer disposed between the anode and the first organic layer and being a non-light emitting layer in direct contact with the first organic layer,
The second organic layer
An organic small molecule hole transporting material having a concentration of 50 to 99% by weight,
And an organic small molecule molecular electron transporting material having a concentration of 0.1 to 5% by weight,
Further comprising a fifth organic layer disposed between the second organic layer and the anode and in direct contact with the second organic layer, wherein the fifth organic layer includes an organic small molecule hole transporting material and does not include an organic small molecule molecular electron transporting material,
Wherein the fifth organic layer comprises the same organic small hole transporting material as the second organic layer,
Wherein the HOMO-LUMO difference of the organic small molecule molecular electron transporting material is lower than the HOMO-LUMO difference of the organic small molecule hole transport material by at least 0.2 eV. The organic light-emitting device according to claim 1, wherein the concentration of the organic small molecule molecular electron transporting material in the second organic layer is 0.1 to 4 wt%. The organic light emitting device according to claim 1, wherein the organic small molecule molecular electron transporting material has a concentration of 0.1 to 3 wt% in the second organic layer. The organic light emitting device according to claim 1, wherein the organic small molecule molecular electron transporting material has a concentration of 2 to 3 wt% in the second organic layer. The organic electroluminescent device according to claim 1, further comprising a third organic layer disposed between the second organic layer and the anode and including a hole injecting material, wherein the third organic layer is in direct contact with the anode and in direct contact with the fifth organic layer Organic light emitting device. The organic light emitting device according to claim 1, further comprising a fourth organic layer disposed between the first organic layer and the cathode, and the fourth organic layer is a light emitting layer including a second light emitting material. The organic light emitting device according to claim 1, wherein the LUMO energy level of the organic small molecule molecular electron transporting material is lower than the LUMO energy level of the organic small molecule hole transporting material by 0.2 eV or more. The organic light-emitting device according to claim 1, wherein the first organic light-emitting material is phosphorescent. The organic light-emitting device according to claim 8, wherein the light-emitting material has a peak emission wavelength in a visible spectrum of 600 to 700 nm. The organic light-emitting device according to claim 8, wherein the light-emitting material has a peak emission wavelength in a visible spectrum of 500 to 600 nm. 9. The organic light emitting device according to claim 8, wherein the light emitting material has a peak emission wavelength in a visible spectrum of 400 to 500 nm. The organic light emitting device according to claim 1, wherein the organic small molecule molecular electron transporting material is metal quinolate. 13. The method of claim 12, wherein an organic small molecule electron-transporting material Alq ₃ in the organic light emitting device. The organic light-emitting device according to claim 1, wherein the organic small molecule hole transporting material is an amine-containing material. 15. The organic light emitting device according to claim 14, wherein the organic small molecule hole transporting material is NPD. The organic light emitting device according to claim 1, wherein the organic small molecule molecular electron transport material has higher electron mobility than the organic small molecule molecular hole transport material. delete delete delete delete

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